[Will]

Ok, so an in-game "test" shows me that simulator ground combat does not work like actual ground combat at all. For simulator, it appears that troops are in a stack (as in the compsci data structure), so that the troops you drop first are the last to be targeted and destroyed, and the troops you drop last are the first to be destroyed.

It appears that actual ground combat works a lot like component selection for ship damage. Add up all the total hitpoints, pick a random number out of that range, and whichever component/troop that falls on, gets destroyed. So, masses of infantry and heavily armored "guard" tanks will soak up most of the troop damage, allowing your high firepower tanks to get in more shots.